Knife Edge help
 

I am flying a Twist and a U Can Do 60 . and I am having problems with getting my knife edge to work . can you help me? Fatuba 9C radio is new to me too.

Also, for my next plane. Is their any 60 size or bigger planes that will fly knife edge well without mixing needed?<br type="_moz" />

RE: Knife Edge help
 

Almost all planes need a little help in knife edge. Even my favorite profile needs a little roll coupling help. The Twist you have is not the best for knife edge. It has a short tail and needs a lot of speed and rudder throw. The UCD should be pretty good in a knife edge.
Can you tell us what it does in knife edge? Or are you asking how to program the radio to mix the roll and pitch out?

David

RE: Knife Edge help
 

I am sure others will help you with regards to radio mixing, I am not too good at that either.

With regards to the second question, you can look at the Venus 60. Its a good pattern-ship that will also do knife-edge well if you do set it up correctly. But its not 3D, doesnt have the surfaces for that. Though I have not flown it myself, I have seen a fellow flier do so

Ameyam

RE: Knife Edge help
 

You haven't told us yet what problem you are having in the knife edge. If it's roll coupling it will just take practice or a mix to overcome it. Simulators are very valuable for practice. As David mentioned, the U can do should be great in a knife edge, but I've not actually flown one.
As far other as planes go, I have two that knife edge better than any other planes I've flown, but neither one is in production right now. The Venus 40 knife edges with ease and very little coupling and I'm told the Venus II flies just like the 40 but easier. The other plane I have the knife edges like its on rails is the Balsa Nova. You can find the Balsa Nova and the Venus 40 for sale from individuals, some times even new in the box, otherwise I'd go for the Venus II.;)

RE: Knife Edge help
 

yes it cups for the gear and I do not know how to mix it out.

RE: Knife Edge help
 

Mixes on the 9C are easy. You need to tell me if you want the mix on all the time or if you want it on a switch? If you want it on a switch, figure out what switch you want it on. I also need to know if you have one or two elev servos. If you do have two servos on the elev, I need to know how they are mixed or if they are on a reverse Y harness or what.
Pulling to the gear can also be a sign of a forward CG. If you roll the plane inverted at 1/2 throttle and let go of the stick, what will it do? If it dives hard your CG could be to far forward.

david

RE: Knife Edge help
 

OS91 with 15x4w prop.        CG 6 "   and still adding washers to tail .            (15 flights so far)    Inverted full thr., I only need a little down ele.<div>No Y harness   , 2 ele. servos              and flap/spoilerons on slider switch</div><div>Yes I think a switch is needed .   </div><div>
</div><div>I do not know what servo wire is were in rx ,  If you want I can dig it out and look.  </div><div>But It seems I need to find my C.G. before I mix anything. Right?</div>

RE: Knife Edge help
 

Right elevator servo is in Ch. 8<div>Left eileron servo  Ch. 6</div><div>Switch E is open?</div>

RE: Knife Edge help
 

Balance (CG) and the resultant trim does affect coupling in KE as well. For example a slilght tail heavy condition calls for more down trim which will couple towards the gear in KE.

Ernie

RE: Knife Edge help
 

The best thing is to start With balancing and trimming this page is great for all of this.

http://www.chinnaero.com/howtos.html

RE: Knife Edge help
 

After you get you CG where it needs to be, here is how to do it.
Open you menu and go "ADVANCE(ACRO) 1/2" this has your "PROG.MIX1 thru7" on it Open mix 1 thru 5. Which ever one you are not using. Go to screen <2/2>. The first screen that opens is <1/2> we will go back to it. The top is MIX> leave it for now. next is MAS> turn this to RUDD. Next is SLV> turn this to ELEV, link&gt;=on,TRIM>=on, SW=E in your case.( In my case I use B because I have dual rates on my rudder there and I have the mix come on using low rate only.) The last place says POSI> this is the position the switch will be when the mix is on. So pick UP or DOWN. IF you choose down then put the switch down and go back up to MIX> It should say INH (inhibit) Turn the knob till it says ON. Then flip your switch E and make sure it comes on and off as you toggle the switch.
Now go back to screen <1/2> This screen will have [PROG.MIX1] , (ON) if your switch is on, (RUDD-> ELEV->) and the next line will be RATE> with 0% on both sides. Moving the rudder stick to the left will highlight the left and the same on the right. Now comes the part you have to figure out. You need to start with 5% both ways but I can't tell you if you need + or -. You need to turn the plane on, have the mix on and move the rudder. Put about 25% + on your mix and see which way the elevs move. Since you are pulling to the belly, the elev halves need to go up. When you have them going up, then move the mix % back down to 5%. This should be a good starting point for you. Every plane is different so you are going to need to tinker with the % I have one, for example, that needs 3% for a left KE and 16% for a right.
One last thing. I still don't know how you are driving your elev servos. So make sure your mix is moving both servos. It is possible you will need a second mix to drive the other elev half. Since we turned the link on earlier you shouldn't, but double check. If the plane rolls in KE. Do the same mix we just did but with AILE as the SLV.

David

RE: Knife Edge help
 

Thank-you so much! I'm busy working,can't fly right now, but will continue next week sometime.

RE: Knife Edge help
 

Not a problem. I watch for you to post if you have any questions.

David

RE: Knife Edge help
 

David, how are you at KE harriers?

Thanks,

Ernie

RE: Knife Edge help
 

reading this has helped me understand how to get my knifies better. thanks.</p>

RE: Knife Edge help
 

Ernie, With the right plane, I am great. The 67" Fusion will do them at a walking pace. I also have a 72" QQ Yak that is pretty good at them. Not as slow as the profile, but very stable. A lot of planes get real bad coupling as the AOA increases and the speed slows down.

Texasclouds, That is great. That is what RCU is for.

David :-)

RE: Knife Edge help
 

Dave, do you hold in full rudder and control the nose with the throttle, or work both the throttle and rudder in those KE harriers??

Thanks,

Ernie

RE: Knife Edge help
 

It's a combination Ernie. Rarely do I ever use full rudder. I start about half power and increse the rudder throw as I decrease the throttle input until I find the sweet spot. It's a balancing act. Plus it is different amounts of each from day to day even with the same plane. The wind,temp and humidity all make a difference. Compared to a normal Harrier you just have a lot less surface area to work with. So you just need to feel your way through it.

David

RE: Knife Edge help
 

I would resist the temptation to try and mix out the inputs you need to fly knife edge if you are A BEGINNER TO KNIFE EDGE FLYING.

WHY one of the things that good 3D pilots learn is how to instinctively correct for these things.

Once you get used to flying in the unusual positions and attitudes of 3D flying and your use of all the controls needed for these corrections is a learned reflex and not requiring thought THEN start with the mixes.

RE: Knife Edge help
 

Thanks guys. Dave, one of the thing's I've noticed about the KE harriers with my early experiences, is that with that reduced surface area you mentioned, steering inputs (w/ elevator) drastically make it want to drop unless you are right on the throttle and ready for that. Right?

Thanks, Ernie

RE: Knife Edge help
 

Any input ,Ernie scrubs off a bunch of airspeed. This is why you get the drop. I use a lot of expo in my elev halves. This helps a little. Once you find the sweet spot you should be able to hold your inputs almost constant and fly the length of the field. If you are going to make laps in that attitude, the your turns will take a little more power and a little less rudder deflection.

david

RE: Knife Edge help
 

David ,  It works !!!   Thank You very much!!<div>
</div><div>You are not going to believe this, On the UCD I needed a temporary prop. So I could get one more flight in. A wood Zinger pro 14x5</div><div>(all I ever used was 4 pitch ) Guess what!   NO MIX WAS NEEDED! perfect knife edge!</div>

RE: Knife Edge help
 

Glad it worked out.

David

RE: Knife Edge help
 

One thing I found helpful in dealing with airplanes that have coupling issues in Knife edge (Daveopam alluded to it earlier) is to not use more rudder input than you need to. For a normal KE pass at speed, it often takes less rudder than you think. Using lots of deflection tends to exponentially (pardon the pun) magnify coupling problems. Of course, HA KE requires more throw....
As to coupling, I like to mix it out so the rudder input yields a neutral response. This really helps when doing moves like rollers in which the interaction between surfaces due to coupling can mess up the roll.

Just my opinionhttp://www.rcuniverse.com/forum/js/f...y/msn/cool.gif

RE: Knife Edge help
 

That's a good point dave45. Another point along those same lines. I was helping a guy learn to knife edge this past Sunday. He was rolling the plane and then adding the rudder. If you do it that way then you have to catch the plane with the rudder. In other words the plane is loosing ALT as you roll. It is going to take more rudder to stop the decent, than it would to hold the ALT. So as I told him, from upright,move your sticks together or apart at the same time. After some practice you can adjust the rate you add the rudder until the plane stays level from normal flight to knife edge. I suggested he practice some slow straight rolls on the sim. He also wants to learn some rolling circles. I suggested he learn the slow roll first. He is a great heli flyer and thought a plane would be easy. lol

david